Recently, in multicarrier transmission systems, user scheduling methods for arranging multiple blocks along frequency axes and time axes have been provided. Regions that are secured when users perform communications and that are defined by frequency axes and time axes are referred to as assignment slots, and blocks forming the basis of assignment blocks, i.e. regions defined by prescribed frequency bands and prescribed time domains, are referred to as chunks.
In this connection, in transmission via broadcast/multicast channels and control channels, blocks that are broadened in frequency axes are assigned so as to get frequency diversity effects, thus making it difficult to cause errors in received signals even when received power is low; and in transmission of unicast signals via one-to-one communications between radio transmitters and radio receivers, blocks that are broadened in frequency axes are assigned so as to get multiuser diversity effects.
FIGS. 31 and 32 are drawings showing the relationships of signals, which are transmitted from radio transmitters to radio receivers, with reference to time (vertical axis) and frequency (horizontal axis). Transmission times t1 to t5 are set to the time axis. The transmission times t1 to t5 are identical to each other in time length. In addition, transmission frequencies f1 to f4 are set to the frequency axis. All the transmission frequencies f1 to f4 have the same frequency band of Fc. Thus, twenty chunks K1 to K20 are set by way of the transmission times t1 to t5 and the transmission frequencies f1 to f4.
By use of the chunks K1 to K20 shown in FIG. 31, as shown in FIG. 31, for example, four chunks K1 to K4 are coupled in the frequency axis and are equally divided into three regions along the time axis, thus setting communication slots S1 to S3, each of which has a time length of t1/3 and a frequency band of 4×f1. The assignment slot S1 is assigned to a first user; the assignment slot S2 is assigned to a second user; and the assignment slot S3 is assigned to a third user. Thus, it is possible for the first to third users to obtain frequency diversity effects.
The chunk K5 is assigned to a fourth user as an assignment slot S4. The chunks K6 and K7 are coupled to form an assignment slot S5, which is assigned to a fifth user. The chunk K8 is assigned to a sixth user as a slot S6. Thus, it is possible for the fourth to sixth users to obtain multiuser diversity effects.
The chunks K9 and K11 are coupled to form an assignment slot S7, which is assigned to a seventh user. The chunks K10 and K12 are coupled and then equally divided into three regions so as to set communication slots S8 to S10, each of which has a time length of t3/3 and a frequency band of 2×f2. The assignment slot S8 is assigned to an eighth user; the assignment slot S9 is assigned to a ninth user; and the assignment slot S10 is assigned to a tenth user. Thus, it is possible for the seventh to tenth users to obtain frequency diversity effects.
The chunk K13 is assigned to an eleventh user as an assignment slot S11. The chunk K14 is assigned to a twelfth user as an assignment slot S12. The chunks K15 and K16 are coupled so as to form an assignment slot S13, which is assigned to a thirteenth user. Thus, it is possible for the eleventh to thirteenth users to obtain multiuser diversity effects.
In addition, the chunks K17 and K19 are coupled so as to form an assignment slot S14, which is assigned to a fourteenth user. The chunks K18 and K20 are coupled and then equally divided into three regions so as to form communication slots S15 to S17, each of which has a time length of t5/3 and a frequency band of 2×f2. The assignment slot S15 is assigned to a fifteenth user; the assignment slot S16 is assigned to a sixteenth user; and the assignment slot S17 is assigned to a seventeenth user. Thus, it is possible for the fourteenth to seventeenth users to obtain frequency diversity effects.    Non-Patent Document 1: 3GPP document, R1-050249, “Downlink Multiple Access Scheme for Evolved UTRA”, [retrieved on Aug. 17, 2005], Internet (URL: ftp://ftp.3gpp.org/TSG_RAN/WG1_RL1/TSGR1—40bis/Docs/R1-050249.zip)    Non-Patent Document 2: 3GPP document, R1-050590, “Physical Channel and Multiplexing in Evolved UTRA Downlink”, [retrieved on Aug. 17, 2005], Internet (URL: ftp://ftp.3gpp.org/TSG_RAN/WG1 RL1/R1_Ad_Hocs/LTE_AH_June-05/Docs/R1-050590.zip)